Leveling instruments, particularly spirit levels, are a well known and valuable tool for those persons engaged in the building and construction field. These instruments generally comprise an elongated straightedge or rule of sufficient thickness to contain one or more level vials. The vials are of generally cylindrical shape, but are slightly curved or of slightly larger diameter in the center to allow the gas bubble contained within the liquid in the vial to seek the center of the vial when the instrument is level.
As noted above, this principle is well known and provides for an accurate and efficient tool due to its inherent simplicity. This simplicity, however, causes some inherent limitations, one of which is the difficulty in accurately reading the instrument in conditions of low light. Typically, no electrical power or installed lighting is available at the time such levels are being used for basic construction alignment. While levels using electric lighting to illuminate the level vial(s) are known, they are not widely used due to various limitations of the illumination systems heretofore provided. Thus, many persons in the field prefer to use a separate source of illumination, such as a flashlight or even a cigarette lighter, to provide the illumination needed to accurately read the instrument in the low light conditions commonly associated with building and construction job sites.
What is needed is an illuminated spirit level incorporating fiber optic light transmission means in order to provide for ease and economy of manufacture. The switch for such a device should be located in a protected location to preclude the accidental actuation of the lighting system and discharging of the battery. The device may also include other functional improvements, such as rechargeable batteries and an adapter plug to permit their recharging without the need for their removal and a timer providing for the automatic shutoff of the circuit after a given time to preclude the accidental discharging of the batteries.